Faraday Cages ... anyone here know much about them?

I’ve been reading up on Faraday Cages as a means of protecting electronic equipment against Electro-Magnetic Pulses ( EMP ). The literature online is mostly explanatory about how the cages work, but not so much about the particulars: can cables pass through the cage without allowing the equipment inside to be affected by an EMP; can you drape an EMP cloth over a small building, or must it completely surround the building on the bottom as well; why, if a car is a faraday cage by construction, does it need a ground, etc.